Sorry I'm slow as usual about getting this.
The only resistance range I see is in the table and it says
Wattage | Resistance Range (W) |
Rating | Standard Type | Non-Inductive Type |
Then the values are like 0.05W - 5KW
Do you mean, I take say "Free Air 100W-150W" which is line 2
At 100C ambient, which is 50% of rated power.
Then resister I would need would be 300W Rating and I can get them
from 0.00067 ohms (0.2W / 300W) to 60 Ohms (18KW /300W)?
Kind of.
Looking at the table, the wattage rating is the column on the left and
indicates that they make resistors in this series with ratings from 60
to 1000 watts. Next to that is a column labelled "Resistance Range
(omega)" which is divided into two columns, one labelled "Standard Type"
and one labelled "Non-Inductive type".
Looking at the first row, there will be an entry in the left-hand
column which reads "60", an entry in the center column which reads
"0.05 omega - 5K omega", and an entry in the third column which reads
"0.1 omega - 2.5k omega", with 'omega' meaning ohms.
The first entry in the center column corresponds to the first entry in
the "Wattage Rating" column and indicates that if you need a standard
(not non-inductive) 60 watt resistor you can get them with resistances
anywhere between 0.05 ohm and 5000 ohms. The first entry in the third
column indicates that they can supply non-inductive 60 watt resistors
with resistances anywhere between 0.1 ohm and 2500 ohms. The rest of
the table follows suit, and serves to show what resistances in standard
and non-inductively wound resistors they can supply at the wattage
ratings they offer.
Their "% of Rated Power" VS "Ambient Temperature" graph is pretty
straightforward and indicates the derating that must be done with the
resistors either on a proper heat sink or in free air at different
ambient temperatures. Let's say for instance that you do your
calculations and find that your resistor will need to dissipate 100W in
free air at an ambient temp of 25°C. Since the second plot down
corresponds to 100W ~ 150W, draw a line vertically starting at 1/4 of
the way from zero to 100°C until it hits the second line and then
continue the line you're drawing horizontally from that point until it
hits the 0 to 100% line. It'll fall somewhere a little bit higher than
70%, so if you use 70% you'll be safe. Now, since you need for the
resistor to dissipate 100 watts and the graph shows that the resistor
needs to be derated to 70% of its rating to dissipate 100W at 25°C, that
means you have to start out with about a 143 watt resistor, so 150 watts
would be a good choice. Now go back and look at the range of
resistances available with a 150W rating and you'll find that they have
from 0.1ohm to 12000 ohms available, so it's probably likely they'll
have what you need. OK?